Mr Hilton told detectives his four friends, Allan Neil Laurie, Allan John "Shorty" Laurie, Terrance James O'Neill, and Larry Charles, arrived at his Toowoomba house on a Sunday morning in late 1974 in the Holden.

The men from two Toowoomba families related through marriage - the Lauries and the Hiltons - had a notorious reputation around town and shared the distinctive green-coloured Holden, he said.

On that morning, Mr Hilton said, the men bragged about giving two young girls a "hiding" at the bottom of the range.

"They said they gave them a hiding ... the same they did every weekend," Mr Hilton said.

He said he found blood smeared across the back seat of the car "as though someone had been dragged across it".

He said he feared also "copping a hiding" if he refused to clean the car.

Lorraine Ruth Wilson (left) and Wendy Joy Evans were found murdered in 1978 after they went missing in 1974. Photo: Wolter Peeters

"You did it or you paid for it later on," he said.

Mr Hilton said Wayne Hilton and Donald "Donny" Laurie were at his home drinking at the time and decided to drive to the bottom of the range to "check on the girls".

"Donny and Wayne came back and said the girls had got a hiding," Mr Hilton said.

Donny returned with blood on his hands, he said.

Ms Wilson and Ms Evans were last seen leaving a relative's home in the Brisbane suburb of Camp Hill in early October 1974 to hitch-hike to Goondiwindi, where they were to pick up a car and drive to Sydney.

Outside court, Debbie Sneddon struggled to contain her grief as she spoke of the loss of her sister Wendy Evans nearly four decades ago.

"They took my best friend away from me,'' she said.

Ms Sneddon was 13 years old, when her older sister vanished, while holidaying in Queensland.